ANAEROBIC RESPIRATION AND FERMENTATION 315 



most of the other theories, it is admitted that since they are col- 

 loidal with enormous surfaces exposed, here also surface phenomena 

 may come into play. The iron is supposed to be either an oxygen 

 carrier or activator, since ordinary molecular oxygen cannot act 

 as a hydrogen acceptor until it has been activated by iron. 



Bach and Chodat, the main features of whose theory were 

 enunciated independently by Engler in the same year (1897), have 

 emphasized the catalytic (enzymic) aspects of respiration. Accord- 

 ing to their scheme of things, for oxidation there must be present 

 oxygenase, a peroxide, and peroxidase. The first named is able to 

 take up oxygen from the air in an active state and thus forms a 

 peroxide. Peroxidases transfer the oxygen from the peroxide to the 

 substance which is to be oxidized. 



That two such enzymes are present is deduced from the fact 

 that expressed juices or extracts from some plants will turn a solu- 

 tion of gum guaiac blue when in the presence of air. Other plants 

 will give the blue reaction only when a few drops of hydrogen 

 peroxide are added. Those of the first group seem, therefore, to 

 contain both an oxygenase (able to get the oxygen from the air) 

 and a peroxidase (able to transfer it to the guaiac); while in the 

 plants of the second group there is a substance present which can 

 transfer the oxygen from the (hydrogen) peroxide to the guaiac, 

 but there is no enzyme present to form the peroxide, which must 

 therefore be added. 



Bach and Chodat have applied this to respiration by assuming 

 that respiration takes place in the following steps (to illustrate 

 from the respiration of glucose) : 



C 6 H 12 6 +6H 2 = 6C0 2 + 12H 2 

 A (oxygenase) +0 2 = A0 2 (peroxide) 

 A0 2 (peroxide) -^O+O (active oxygen) + A (oxygenase) 



2H 2 +0 2 = 2H 2 0. 



Thus in the plant the sugar of the cell unites with water to 

 form carbon dioxide and hydrogen. The oxygenase takes up 

 oxygen from the air to form the organic peroxide, which is split 

 up by the peroxidase to reform the oxygenase and active oxygen, 

 which in turn easily combines at low temperatures with the hy- 

 drogen to form water. This explains the visible results as seen in 

 the experiments with the oxidases, and further explains why water 

 is so important in respiratory processes. The food actually com- 



